Which of the following processes does not involve a catalyst?

If the foci of the ellipse $\frac{x^2}{16} + \frac{y^2}{b^2} = 1$ and the hyperbola $\frac{x^2}{144} - \frac{y^2}{81} = \frac{1}{25}$ are the same,then the value of $b^2$ is:

$A$ ball of mass $m_1$ and another ball of mass $m_2$ are dropped from the same height. If the time taken by the balls to reach the ground is $t_1$ and $t_2$ respectively,then:

The centre of mass of a body

Smoke is an example of ...

The solution of the differential equation $\frac{dy}{dx} = \frac{xy+y}{xy+x}$ is